1. Technical Field
The present invention relates to a solid-state imaging device including an optical waveguide and a method for manufacturing the same.
2. Background Art
In recent years, in connection with solid-state imaging devices, miniaturization of pixels has been promoted due to an increase in the number of pixels. In association therewith, miniaturization of a light receiving portion has been promoted, which causes difficulties to each light receiving portion in maintaining its high sensitive performance. Addressing this problem, what are proposed are solid-state imaging devices in which an optical waveguide is provided on a photodiode being a light receiving portion (for example, see Unexamined Japanese Patent Publication No. 2008-166677). Since the optical waveguide is structured with a material whose refractive index is high, the incident light can efficiently be propagated to the photodiode without being leaked to the outside of the optical waveguide.
FIG. 10 shows a cross-sectional structure of a semiconductor device according to a conventional example disclosed in Unexamined Japanese Patent Publication No. 2008-166677. As shown in FIG. 10, in pixel portion RPX, an optical waveguide is formed in concave portion H above photodiode PD so as to penetrate through layered insulating films 21, 22, 25 and others. In the optical waveguide, a buried insulating film (passivation film 36) and a resin film (buried layer 37) containing metal oxide whose refractive index is high are formed. Unexamined Japanese Patent Publication No. 2008-166677 discloses that, the optical waveguide is formed by, in concave portion H whose opening dimension is 0.8 μm and aspect ratio is approximately 1 to 2 or more, forming passivation film 36 that is made of silicon nitride or the like, that has a refractive index of 2.0, and that has a thickness of approximately 0.5 μm. Further, the optical waveguide is formed by embedding buried layer 37 made of resin whose refractive index is high, such as siloxane-base resin (refractive index 1.7), polyimide or the like.
Here, it is disclosed that passivation film 36 is thickly deposited on the edge portion of concave portion H and becomes thinner near the bottom portion because of anisotropy when it is deposited.
In peripheral circuit portion RPAD, passivation film 36 and buried layer 37 are formed on pad electrode 32 made of aluminum. That is, according to the manufacturing method of the conventional example, after an aluminum interconnection including pad electrode 32 is formed, concave portion H to be the optical waveguide is formed. Then, concave portion H is sequentially filled with passivation film 36 and buried layer 37 to form the optical waveguide.
Passivation film 36 is made of silicon nitride formed by the chemical vapor deposition (CVD) process, and as described above, the refractive index thereof is approximately 1.9 to 2.0. On the other hand, buried layer 37 is made of resin formed by the application process, and as described above, the refractive index thereof is approximately up to 1.7.